Nonwoven fabrics or webs, alone or as a laminate with other nonwovens or films, constitute all or part of numerous commercial products including disposable absorbent products such as adult incontinence products, sanitary napkins, disposable diapers, and training pants. Other commercial products include wipers, protective garments, and surgical gowns. Nonwoven fabrics have been used in the manufacture of such personal care products because it is possible to produce them with desirable cloth-like aesthetics at a low cost. The elastic properties of some nonwoven fabrics have allowed them to be used in form-fitting garments, and their flexibility enables the wearer to move in a normal, unrestricted manner.
Nonwoven fabrics or webs have a physical structure of individual fibers, strands or threads which are interlaid, but not in a regular, identifiable manner as in a knitted or woven fabric. The fibers may be continuous or discontinuous, and are frequently produced from thermoplastic polymer or copolymer resins from the general classes of polyolefins, polyesters and polyamides, as well as numerous other polymers. Fibers from blends of polymers or conjugate multicomponent fibers may also be employed. Methods and apparatus for forming fibers and producing a nonwoven web from synthetic fibers include meltblowing, spunbonding and carding. Physical properties such as strength, softness, elasticity, absorbency, flexibility and breathability are readily controlled in making nonwovens. However, certain properties must often be balanced against others. An example would be an attempt to lower costs by decreasing fabric basis weight while maintaining reasonable strength.
Films are another common component in many commercial products such as trash bags, diaper backsheets, packaging materials, elastic components, and apertured films such as topsheets. Other films are used as a breathable barrier layer for increased comfort. Breathable microporous films comprise filled films which include a thermoplastic polymer and filler. These and other films can be formed by any one of a variety of film forming processes known in the art including extruding, casting or blowing.
It is widely recognized that properties relating to strength, softness, stretch and/or extensibility of nonwoven fabrics and films are desirable for many applications. Softness can be improved by various mechanical steps including stretching of the nonwoven to break secondary bonds that tend to stiffen the material. Stretch or extensibility of the material can also be improved by stretching the web as it passes between activation rolls. Activation rolls have teeth and grooves which intermesh at a nip having an activation path length. Typical roll on roll activation tooling have an activation path length in the range of 0.5 inches or less. Commercial film, nonwoven, and product making processes are often desired to be run at the highest possible line speeds to create lower manufacturing costs. As a result, stretching resulting from the activation can occur at high rates of strain, which depending on the nature of the material, can result in damage to the final product.
With the ever increasing drive to reduce material cost, the industry is continuously looking for ways of reducing basis weight or substituting lower cost materials in consumer products while maintaining desirable properties such as strength, softness, elasticity, absorbency, flexibility and breathability. Materials typically lacking such properties can attain them through activation; however, some materials including some polypropylenes, polyethylenes, polyesters, and cellulosics are unable to withstand the high rate of strain required for commercial production. Therefore, the need exists for processes and equipment capable of performing mechanical activation on low cost materials at relatively high processing line speeds.